The present invention relates to a system for automatically defining the minimum (i.e. closed) setting of a valve controlled by an accelerator for regulating air supply to an internal combustion engine, in particular, a throttle valve located at the inlet of an induction manifold on an electronic injection system.
Electronic injection systems on internal combustion engines are known to present an electronic control system which, depending on signals received from various sensors (mainly engine speed/stroke and air intake pressure/temperature sensors) determines, for example, the air density in the manifold and engine speed, and calculates, via interpolation on respective memorized maps, the stroke and timing for injecting fuel into the injectors, as well as the spark lead. Provision may be made for one of the said injectors on each cylinder, i.e. located downstream from the throttle valve, or for a single injector located upor downstream from the said throttle valve. For determining specific operation of the electronic control system, particularly during transient states, the said control system is supplied with signals from additional sensors, such as a throttle angle sensor, which also indicates the minimum (substantially closed) setting of the valve. The throttle angle transducer usually empolyed is a potentiometer connected mechanically to the valve spindle, the electric output signals from the potentiometer being supplied to an analogue-digital converter which supplies the throttle setting signal to the control system. Such known solutions, however, involve a number of drawbacks in terms of precise indication of the said minimum setting, particularly long-term precision, which may be affected by incorrect positioning of the potentiometer on the valve spindle, or by other sources of error due to thermal drift, mechanical wear, etc.